STRUCTURES USED IN DRAINING AGRICULTURAL LAND 7 
animals. Heavy galvanized wire with meshes of one-third or one- 
fourth inch will exclude everything but fine debris, and the tile 
line can be inspected readily by reflecting light toward the bottom 
with a mirror. 
CRADLES 
In soft ground some means must be provided for holding the tile 
in alignment. The best method consists of excavating the trench 
below grade and tamping in gravel until a firm foundation is made. 
Boards may be laid under small drains where the bottom of the 
trench is not too soft. They should be fastened together at each 
joint by short strips underneath. 
In verv soft ground cradles on piling may be required. For 
small drains they can be made of two parallel 2 by 4 inch stringers 
held together by 1-inch cross boards. The upper inside corners 
of the stringers should be beveled, and they should be so spaced 
that the tile will bed firmly on them. The cross strips should be 
arranged so that overlapping will occur at each joint. At the up- 
stream end of each set of stringers the crosspiece should extend 
at least 6 inches beyond the stringers, with the grain parallel to 
the stringer, but the other two crosspieces should be nailed on with 
the grain at right angles to the stringers (pi. 1 C). The sections 
should be nailed together at the joints and to the piles, on which 
the crosspieces must rest. This work often has to be done under 
several inches of thin mud; but the nails or spikes may be easily 
driven if inserted in a short section of small pipe, by striking the 
nail head with a rod that fits snugly in the pipe. 
For tile larger than 8 inches the stringers must be made of 4 by 4 
inch timbers fastened together with planks as shown in Figure 5. 
The upper inside corners should be beveled, and they should be 
spaced so that the tile will be supported as nearly as possible at its 
quarter points. When pipe with bell ends is used, notches must 
be cut in the timbers. Joints of the stringers should be staggered 
and cross sills at joints should be 2 by 6 inch planks. Usually it 
is difficult to cut off the tops of piles in the bottom of a trench, 
but sometimes piles of the same or a gradually changing length 
may be used where conditions can be anticipated closely. The driv- 
ing may then be stopped at the proper point to support the cradle. 
In difficult construction it is not expedient to open a long line 
of trench ahead of the tile. For this reason and because of the 
many braces in the trench, cradles made up in short sections must 
be used. Their length should have some relation to the length of 
the sets used in sheeting the trench. 
ANGLE BOXES 
At angle points on main drains, not sharp enough to call for a man- 
hole, an angle box should be made of a pipe somewhat larger than 
the diameter of the tile, extending from a point a few inches below 
the bottom of the tile to the ground surface ; and a small drop should 
be provided between the inlet and outlet. A corrugated iron pipe 
is desirable for this purpose. Angle boxes are sometimes made of 
large sewer pipe at the bottom, above which is placed a reducer and 
then a stack of 8 or 12-inch pipe extending to the top, which can 
